Solid state optoelectronic device with preformed metal support substrate

ABSTRACT

A wafer-level process for manufacturing solid state lighting (“SSL”) devices using large-diameter preformed metal substrates is disclosed. A light emitting structure is formed on a growth substrate, and a preformed metal substrate is bonded to the light emitting structure opposite the growth substrate. The preformed metal substrate can be bonded to the light emitting structure via a metal-metal bond, such as a copper-copper bond, or with an inter-metallic compound bond.

TECHNICAL FIELD

The present technology is directed to solid state lighting (“SSL”)devices constructed on large-diameter wafers (e.g., greater than 4inches) with a preformed metal support substrate.

BACKGROUND

SSL devices generally use semiconductor light emitting diodes (“LEDs”)and/or polymer light emitting diodes (“PLEDs”) as sources ofillumination rather than electrical filaments, a plasma, or a gas.Mobile phones, laptop computers, digital cameras, MP3 players, and otherportable electronic devices can utilize SSL devices for backgroundillumination. SSL devices can also be used for signage, indoor lighting,outdoor lighting, and other types of general illumination.

FIG. 1 shows a conventional vertical SSL device 10 including a lightemitting structure 17 having a p-type gallium nitride (GaN) 12,GaN/indium gallium nitride (InGaN) multiple quantum wells (MQW) 14, andan n-type GaN 16 in series. The SSL device 10 also includes a supportsubstrate 18 and a p-type contact 20 between the support substrate 18and the p-type GaN 12. Conventional support substrates 18 are typicallysapphire or a semiconductor material having a wafer form factor. The SSLdevice 10 also includes an n-type contact 22 on top of the SSL device 20that can be wirebonded to an external contact 24. The SSL device 10 canbe mounted to an external host device 26. As a voltage is appliedbetween the n-type contact 22 and the p-type contact 20, electricalcurrent passes through the light emitting structure 17 and produceslight. The SSL device 10 can be made on a wafer that is singulated intoindividual SSL devices.

Conventional devices use thermo-compression bonding, such ascopper-copper (Cu—Cu) bonding, or eutectic bonding (AuSn), orintermetallic compound (IMC) bonding (NiSn), to attach the lightemitting structure 17 to the support substrate 18. This process requireshigh temperatures and pressures that can bow or deform the wafer to suchan extent that it cracks or warps. Currently LED industry is mostlyworking with 2-4 inch diameter substrates, which limits the throughputand increases costs because fewer SSL devices can be produced on suchsmall wafers. Even at these diameters warp and bow of the wafers is aproblem for fabrication of LEDs. This problem becomes severe for largediameter (>4 inch) wafers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a vertical SSL device according to the prior art.

FIG. 2 illustrates a wafer comprising several SSL devices that include alight emitting structure and a preformed metal substrate according to anembodiment of the present technology.

FIG. 3 illustrates a growth substrate and a light emitting structure fora wafer according to an embodiment of the present technology.

FIG. 4 illustrates a wafer including a light emitting structure havingmetal bonding materials deposited on the light emitting structureaccording to an embodiment of the present technology.

FIG. 5 illustrates a sheet of material having wafer-sized circularblanks stamped from the sheet.

FIG. 6 illustrates a preformed metal substrate and temporary carrieraccording to an embodiment of the present technology.

FIG. 7 illustrates a preformed metal substrate being bonded to a waferaccording to an embodiment of the present technology.

FIG. 8 illustrates a wafer having a preformed metal substrate and lightemitting structure according to an embodiment of the present technology.

FIG. 9 illustrates a preformed metal substrate bonded to a lightemitting structure via an inter-metallic compound (“IMC”) bond accordingto an embodiment of the present technology.

FIG. 10 illustrates a preformed metal substrate having an IMC stackformed thereon according to an embodiment of the present technology.

FIG. 11 illustrates the preformed metal substrate of FIG. 10 beingbonded to a light emitting structure of a wafer according to anembodiment of the present technology.

FIG. 12 illustrates a preformed metal substrate having first IMCcomponents formed thereon and a light emitting structure having secondIMC components formed thereon according to an embodiment of the presenttechnology.

FIG. 13 illustrates an IMC bond between a preformed metal substrate anda light emitting structure according to an embodiment of the presenttechnology.

FIG. 14 illustrates a preformed metal substrate being bonded to a lightemitting structure, wherein the light emitting structure contains IMCcomponents to form an IMC bond between the preformed metal substrate andthe light emitting structure.

DETAILED DESCRIPTION

Various embodiments of SSL devices, assemblies, and methods ofmanufacturing are described below. As used hereinafter, the term “SSLdevice” generally refers to devices with LEDs, laser diodes (“LDs”),PLEDs, organic light emitting diodes (“OLEDs”), and/or other suitablelight emitting structures other than electrical filaments, a plasma, ora gas. A person skilled in the relevant art will also understand thatthe technology may have additional embodiments and that the technologymay be practiced without several of the details of the embodimentsdescribed below with reference to FIGS. 2-14.

FIG. 2 illustrates a wafer 100 comprising a plurality of SSL devices 110formed at the wafer level according to selected embodiments of thepresent technology. It is to be appreciated that some of the processesdescribed herein can be selectively applied to portions of the wafer 100or to the entire wafer 100. The wafer 100 can have a generally circularshape with a diameter of at least four inches, and in many embodimentsthe wafer diameter can be 6-8 inches or larger. In selected embodiments,the wafer 100 includes a preformed metal substrate 120 bonded to a lightemitting structure 130 and an exterior contact 140 on the light emittingstructure 130. As explained in more detail below, the preformed metalsubstrate 120 can be a metal blank or plate that is formed apart fromthe light emitting structure 130 and then bonded to the light emittingstructure 130. The preformed metal substrate 120 has a sufficientthickness to inhibit bowing of the light emitting structure 130. Forexample, when the light emitting structure 130 has a diameter of atleast 100 mm (e.g., 100 mm, 150 mm, 200 mm, 300 mm, or more), thepreformed metal substrate 120 alone without another carrier or supportsubstrate can inhibit bowing at the center of the wafer 100 to less thanabout 10 μm⁻¹⁰⁰ mm, or less than about one of 500 μm, 100 μm, 50 μm, 20μm, 10 μm or 5 μm (e.g., 0.001% to 1%).

The preformed metal substrate 120 can be electrically and thermallyconductive. For example, the preformed metal substrate 120 can be anelemental metal, an alloy of different metals, or a plurality ofnon-alloyed metals. In one embodiment, the preformed metal substrate 120includes copper, a copper alloy, aluminum, and/or other metals.

The light emitting structure 130 can be an LED, a PLED, an OLED, oranother solid state structure that includes a first semiconductormaterial 132, a second semiconductor material 134, and an active region136 between the first semiconductor material 132 and the secondsemiconductor material 134. In one embodiment, the first and secondsemiconductor materials 132 and 134 include a p-type GaN material and ann-type GaN material, respectively. In another embodiment, the first andsecond semiconductor materials 132 and 134 include an n-type GaNmaterial and a p-type GaN material, respectively. In furtherembodiments, the first and second semiconductor materials 132 and 134can individually include at least one of gallium arsenide (GaAs),aluminum gallium arsenide (AlGaAs), gallium arsenide phosphide (GaAsP),gallium (III) phosphide (GaP), zinc selenide (ZnSe), boron nitride (BN),aluminum gallium nitride (AlGaN), and/or other suitable semiconductormaterials.

The active region 136 can include a single quantum well (“SQW”),multiple quantum wells (“MQWs”), and/or a bulk semiconductor material.As used hereinafter, a “bulk semiconductor material” generally refers toa single grain semiconductor material (e.g., InGaN) with a thicknessgreater than about 10 nanometers and up to about 500 nanometers. Incertain embodiments, the active region 136 can include an InGaN SQW,InGaN/GaN MQWs, and/or an InGaN bulk material. In other embodiments, theactive region 136 can include aluminum gallium indium phosphide(AlGaInP), aluminum gallium indium nitride (AlGaInN), and/or othersuitable materials or configurations. In any of the foregoingembodiments, the first semiconductor material 132, the active region136, the second semiconductor material 134, and any buffer materials(not shown) can be formed via metal organic chemical vapor deposition(“MOCVD”), molecular beam epitaxy (“MBE”), liquid phase epitaxy (“LPE”),hydride vapor phase epitaxy (“HVPE”), and/or other suitable epitaxialgrowth techniques.

The wafer 100 can also have an electrode 150 electrically coupled to thefirst semiconductor material 132. In other embodiments, the electrode150 can be omitted and a portion of the preformed metal substrate 120can be used as an electrode lead electrically coupled to the firstsemiconductor material 132. The exterior contact 140 and light emittingstructure 130 can form a vertically oriented SSL device 110 as definedabove. In many configurations, the p-type components and the n-typecomponents are transposed, and the SSL devices 110 can have otherconfigurations, such as lateral configurations.

FIGS. 3-8 illustrate methods and procedures for forming the wafer 100according to selected embodiments of the present technology. At thestage shown in FIG. 3, the wafer 100 includes a growth substrate 160 andthe light emitting structure 130 on the growth substrate 160. The growthsubstrate 160 can include silicon (Si) with a Si(1,1,1) crystalorientation at the surface upon which the light emitting structure 130is formed. In other embodiments, the growth substrate can include AlGaN,GaN, silicon carbide (SiC), sapphire (Al₂O₃), an engineered substrate, acombination of the foregoing materials, and/or other suitable substratematerials. The light emitting structure 130 can be the same as describedabove in FIG. 2. In the embodiment of FIG. 3, the second semiconductormaterial 134 is grown on or proximate the growth substrate 160, and thenthe active region 136 and first semiconductor material 132 are thengrown sequentially.

FIG. 4 illustrates a further stage of the method according to thepresent technology after a metal bonding structure 170 is formed on thelight emitting structure 130. In selected embodiments, the metal bondingstructure 170 comprises a metal stack that forms an embedded electrode(e.g., embedded electrode 150 shown in FIG. 2) and/or provides a barriermaterial and/or reflective material. The metal bonding structure 170 canalso have a copper seed material deposited on the metal stack. Thecopper seed material can later be used to form an additional metalstructure on the seed material through a process such as electroplating.For example, the metal bonding structure 170 can include a reflectivematerial 172 (e.g., silver (Ag) or aluminum (Al)), a barrier material174 (e.g., tungsten titanium (WTi) or tantalum nitride (TaN)), and acopper seed layer 176. Other suitable metals can be used, and the metalbonding structure 170 can be formed using suitable techniques known inthe art.

FIG. 5 illustrates a separate stage performed apart from forming thelight emitting structure 130 in which a metal sheet 180, such as acopper sheet, is stamped or otherwise fabricated to form a plurality ofmetal blanks 182 that have approximately the same diameter or other formfactor dimension as the wafer 100. After being fabricated from thesheet, each metal blank 182 can define an individual preformed metalsubstrate configured to be attached to a light emitting structure, suchas the preformed metal substrate 120 shown in FIG. 2. The pattern of themetal blanks 182 relative to the sheet 180 can vary, and the metalblanks 182 can be formed individually rather than being fabricated froma sheet. The metal blanks 182 can be formed to have sufficient thicknessto support and inhibit bowing of the light emitting structure 130. Inselected embodiments, the thickness of the metal blanks 182 can beapproximately, for example, 50-300 μm, 150-300 μm, 100-150 μm, or 75-150μm. In selected embodiments, the metal blanks 182 are thick enough to behandled and incorporated into the wafer 100 without bowing and withoutbeing supported by another support structure.

FIG. 6 illustrates an embodiment of a preformed metal substrate 120 madefrom a metal blank 182 that has been attached to a temporary carrier 186by an adhesive 184. The temporary carrier 186 is preferable for thinnerpreformed metal substrates 120 that are difficult to handle due to theirsize. The temporary carrier 186 can be made of an inexpensive material,such as silicon or a carrier tape, that can be reused and/or recycled.

FIG. 7 shows a further stage in which the preformed metal substrate 120is bonded to the metal bonding structure 170 using a metal-metal bond.In embodiments in which the metal bonding structure 170 and thepreformed metal substrate 120 both include copper, the two metals can bebonded together with a copper-copper (Cu—Cu) bond. The metal bondingstructure 170 and the preformed metal substrate 120 can also eachinclude materials for forming an intermetallic compound (IMC) oreutectic bond. These embodiments are discussed in more detail below.

FIG. 8 illustrates the wafer 100 in an inverted orientation after thepreformed metal substrate 120 and the metal bonding structure 170 havebeen bonded together such that the preformed metal substrate 120 is atthe base of the wafer 100. The growth substrate 160 (shown in phantom)can be removed from the light emitting structure 130 by grinding,post-grinding, wet etching, dry etching, or another suitable process.The exterior contact 140 can be formed on the light emitting structure130 using a suitable metal evaporation and patterning technique. Theexterior contacts 140 can be patterned as needed, and each SSL device110 can have one or more exterior contacts 140. For embodiments in whichthe second semiconductor material 134 includes N—GaN, the exteriorcontacts 140 can be made of a titanium-aluminum stack (e.g., Ti/Al orAl/Ti/Al). The wafer 100 can be further processed in an annealing stepand with a surface-roughening procedure. The temporary carrier 186 (notshown in FIG. 8) can be removed from the wafer 100 using similarprocesses that were used to remove the growth substrate 160, or thermaldebonding, or in the case of a tape the temporary carrier 186 can bepeeled off of the wafer 100.

In selected embodiments, the metal-metal bond between the preformedmetal substrate 120 and the metal bonding structure 170 can be made at asuitable temperature to avoid harming any existing bonds or otherstructures on the wafer 100. Also, some temporary bonds made at onetemperature can be debonded at a different temperature. Thischaracteristic is used advantageously in several embodiments of methodsin accordance with the present technology. For example, the preformedmetal substrate 120 can be bonded to the temporary carrier 186 at afirst temperature (T₁) and debonded at a second temperature (T₂). Inseveral applications, T₁ can be approximately the same as T₂. Thepreformed metal substrate 120 can also be bonded to the light emittingstructure 130 at a third temperature (T₃) and debonded at a fourthtemperature (T₄). In one embodiment, the bonding temperature T₃ betweenthe preformed metal substrate 120 and the light emitting structure 130is less than the debonding temperature T₂ between the preformed metalsubstrate 120 and the temporary carrier 186 so that bonding thepreformed metal substrate 120 to the light emitting structure 130 doesnot debond the preformed metal substrate 120 from the temporary carrier186. Additionally, the debonding temperature T₂ between the preformedmetal substrate 120 and the temporary carrier 186 is less than thedebonding temperature T₄ between the light emitting structure 130 andthe preformed metal substrate 120 so that the temporary carrier 186 canbe removed without debonding the preformed metal substrate 120 from thelight emitting structure 130. As such, in this embodiment, T₃<T₂<T₄. Thematerials and bonding processes should be selected to satisfy theseconditions.

One specific example that meets these conditions, which is not intendedto be limiting, uses a high-temperature thermoplastic temporary bond forbonding the preformed metal substrate 120 to the temporary carrier 186.The thermoplastic temporary bond material can be polyether-etherkeytone(PEEK) or a PEEK-based material with a melting point greater than about320° C. The metal-metal bonds, such as between the metal bondingstructure 170 and the preformed metal substrate 120, can be made astemporary liquid phase (“TLP”) bonds. Examples of bonding materials thatsatisfy the above-noted constraints are nickel-tin (NiSn, bonds at 300°C., remelts at 796° C.), indium-gold (InAu, bonds at 200° C., remelts at580° C.), and copper-tin (CuSn, bonds at 250° C., remelts at 415° C.).Other temporary and metal-metal bonds can be used as well. Inembodiments in which a high temperature bonding process does not putother bonds at risk, such as when the temporary carrier 186 is not used,any conventional bonding process can be used to bond the metal bondingstructure 170 to the preformed metal substrate 120. For example, ahigh-temperature copper-copper (CuCu), nickel-tin (NiSn), gold-tin(AuSn), copper-tin (CuSn), or other metal bonds can be used withoutrisking harm to the bond between the preformed metal substrate 120 andthe temporary carrier 186.

FIG. 9 illustrates an embodiment of another method in accordance withthe present technology. In selected embodiments, a wafer 200 comprises apreformed metal substrate 220, an IMC bond 222, a light emittingstructure 230, and exterior contacts 240 formed over individual SSLdevices 210 of the wafer 200. Portions of the preformed metal substrate220 can be used as a base contact for the light emitting structure 230.The wafer 200 can be circular having a diameter of at least four inches,and in many cases 6-8 inches or more.

The IMC bond 222 can be made of two materials that bond together to forma metal structure containing an alloy of the two materials. The IMC bond222 can have one boundary region 223 proximate to the preformed metalsubstrate 220, another boundary region 223 proximate the light emittingstructure 230, and a median region 224 between the two boundary regions223. The boundary region 223 can have a higher concentration of one ofthe two materials of the IMC bond 222 compared to the median region 224.The median region 224 can be an alloy or a more uniform mixture of themetals. The resultant bond is strong and relatively inexpensive toproduce.

FIGS. 10-14 illustrate selected stages of a process for manufacturingthe wafer 200 according to embodiments of the present technology. FIG.10 shows a preformed metal blank 282 that defines the preformed metalsubstrate 220 (FIG. 9) attached to a temporary carrier 286. Thepreformed metal substrate 220 can be stamped or otherwise fabricatedfrom a material to have a diameter or other form factor dimension thatsubstantially matches that of the wafer 200. The preformed metalsubstrate 220 can be attached to the temporary carrier 286 with anadhesive 284 or by another suitable means, such as a PEEK bond. Thetemporary carrier 286 may be used when the preformed metal substrate 220is not sufficiently thick to be handled safely without support. Thepreformed metal substrate 220 can have a seed material (not shown)deposited on a surface opposite the temporary carrier 286. Additionalbonding materials 290 can be plated or otherwise deposited on the seedmaterial. In selected embodiments, the bonding materials 290 comprisesequentially plated IMC bonding materials of a first nickel 291, a firsttin 292, a second tin 293, and a second nickel 294. Other combinationsof IMC materials can be used. The relative thicknesses of the variousbonding materials 290 can be designed to minimize lateral strain causedby the disparate properties of the adjacent materials. For example,because some materials tend to expand or contract during the IMCprocess, by creating the stack of bonding materials 290 having the rightmixture of contracting and expanding materials can reduce lateral strainand bowing of the wafer 200.

FIG. 11 shows a stage of the processes of the present technology inwhich the light emitting structure 230 is bonded to the preformed metalsubstrate 220. The light emitting structure 230 can have a thin metalstructure (not shown) which in turn can be bonded to the IMC stack ofbonding materials 290. The orientation of the preformed metal substrate220 and temporary carrier 286 (if present) is such that the preformedmetal substrate 220 is proximate to the light emitting structure 230 andthe temporary carrier 286 is positioned distally away from the lightemitting structure 230. The temporary carrier 286 and a growth substrate260 can then be removed, exterior contacts (shown in FIG. 9) can beformed, and the SSL devices 210 can be singulated from each other.

FIG. 12 illustrates another embodiment of the technology in which thebonding materials are formed in two portions: a first portion 295 on thepreformed metal substrate 220 and a second portion 296 on the lightemitting structure 230. In selected embodiments, the first portion 295includes the first nickel 291 and the first tin 292, and the secondportion 296 includes the second tin 293 and the second nickel 294. IMCbonding can include a broad range of different materials; the examplesgiven here are not intended to limit the scope of the technology to thematerials specifically described herein.

As shown in FIG. 13, the first portion 295 (FIG. 12) and the secondportion 296 (FIG. 12) can be bonded together to form the IMC bond 222 bybringing the first portion 295 and the second portion 296 into contactwith one another and subjecting them to heat and/or pressure that causesthe first and second portions 295, 296 to bond. The growth substrate 260and the temporary carrier 286, if present, can be removed using avariety of procedures including back grinding, etching, orchemical-mechanical polishing (“CMP”) procedures.

FIG. 14 illustrates a further embodiment of the present technology inwhich the IMC bonding materials 290 are formed on the light emittingstructure 230. The process for forming the bonding materials 290 and theeventual IMC bond can be similar to the process described above withreference to FIGS. 10 and 11.

Several embodiments of the wafer 200 made with the techniques describedabove are less expensive than other processes because, at least in part,the preformed metal substrate 220 can be formed with relatively littleexpense. The wafers 100, 200 and the SSL devices 110, 210 produced fromthe wafers 100, 200 are more rigid (less susceptible to bowing) thanconventional devices, and the bonded preformed metal substrates 120, 220also offer excellent thermal and electric conductivity.

From the foregoing, it will be appreciated that specific embodiments ofthe technology have been described herein for purposes of illustration,but that various modifications may be made without deviating from thetechnology. In addition, many of the elements of one embodiment may becombined with other embodiments in addition to or in lieu of theelements of the other embodiments. Accordingly, the technology is notlimited except as by the appended claims.

I claim:
 1. A method of manufacturing a plurality of solid statelighting (“SSL”) devices, the method comprising: forming a metal bondingstructure on a light emitting structure; and bonding a preformed metalsubstrate to the metal bonding structure, wherein the preformed metalsubstrate has a thickness sufficient to decrease bowing of the lightemitting structure, wherein the bonding is based at least in part onheat; and attaching the preformed metal substrate to a temporary carrierwith an adhesive before bonding the preformed metal substrate to themetal bonding structure, wherein— the adhesive forms a bond at a firsttemperature (T₁) and maintains the bond up to at least a secondtemperature (T₂) is debonding, the second temperature (T₂) is greaterthan about 300° C., the preformed metal substrate and the light emittingstructure are bonded together with a metal-to-metal bond that is formedat a third temperature (T₃) and that debonds at a fourth temperature(T₄), the third temperature (T₃) is less than the second temperature(T₂), and the second temperature (T₂) is less than the fourthtemperature (T₄).
 2. The method of claim 1 wherein bonding the preformedmetal substrate to the metal bonding structure comprises bonding apreformed metal substrate having a diameter of at least approximatelyfour inches.
 3. The method of claim 1 wherein the first temperature (T1)is at least approximately equal to the second temperature (T2).
 4. Themethod of claim 1 wherein the preformed metal substrate has a thicknessof about 50-300 μm.
 5. The method of claim 1, further comprising formingthe preformed metal substrate by stamping the preformed metal substratefrom a metal sheet.
 6. The method of claim 1 wherein the light emittingstructure comprises an n-GaN material, a p-GaN material, and a multiplequantum well structure between the n-GaN material and the p-GaNmaterial, wherein the n-GaN material is proximate a growth substrate. 7.The method of claim 1 further comprising forming a barrier material onthe light emitting structure between the light emitting structure andthe metal bonding structure.
 8. The method of claim 1 wherein the metalbonding structure and the preformed metal substrate comprise copper, andwherein bonding the preformed metal substrate to the metal bondingstructure comprises a copper-copper bond.
 9. The method of claim 1wherein bonding the preformed metal substrate to the metal bondingstructure comprises forming an inter-metallic compound bond made ofnickel and tin between the metal bonding structure and the preformedmetal substrate.
 10. The method of claim 1, further comprising formingan inter-metallic compound (“IMC”) stack on the preformed metalsubstrate, and wherein bonding the preformed metal substrate to themetal bonding structure comprises forming an IMC bond between the IMCstack and the metal bonding structure.
 11. The method of claim 1 whereinthe second temperature (T₂) is greater than about 320° C.
 12. The methodof claim 1 wherein the third temperature (T₃) is less than about 300° C.13. The method of claim 1 wherein the adhesive include polyetherkeytone.14. The method of claim 1 wherein the third temperature is about 250° C.or less.
 15. The method of claim 1 wherein the second temperature (T₂)is greater than about 320° C., and wherein the third temperature (T₃) isless than about 300° C.
 16. A method of manufacturing a plurality ofsolid state lighting (“SSL”) devices, the method comprising: forming ametal bonding structure on a light emitting structure, wherein formingthe metal bonding structure comprises forming first inter-metalliccompound (“IMC”) components on the light emitting structure, formingsecond IMC components on the preformed metal substrate; and bonding apreformed metal substrate to the metal bonding structure, wherein thepreformed metal substrate has a thickness sufficient to decrease bowingof the light emitting structure, wherein the bonding is based at leastin part on heat, and wherein— the preformed metal substrate is attachedto a temporary carrier with an adhesive before bonding the preformedmetal substrate to the metal bonding structure, wherein the adhesivemaintains a bond up to a debonding temperature of at least about 300°C., and bonding the preformed metal substrate to the metal bondingstructure comprises bonding the first IMC components to the second IMCcomponents via metal bonding with a bonding temperature below thedebonding temperature.
 17. A method of manufacturing a plurality ofsolid state lighting (“SSL”) devices on a large diameter wafer, themethod comprising: forming a first inter-metallic compound (“IMC”) stackon a light emitting structure, wherein the light emitting structurecomprises a first semiconductor material, a second semiconductormaterial, and an active region between the first and secondsemiconductor materials; forming a second IMC stack on a preformed metalsubstrate, wherein the preformed metal substrate is formed separatelyfrom the light emitting structure and has a thickness sufficient toinhibit bowing of the light emitting structure; attaching the preformedmetal substrate to a temporary carrier with an adhesive having adebonding temperature of at least 300° C.; and bonding the first IMCstack to the second IMC stack such that the preformed metal substrate isattached to the light emitting structure, and such that the preformedmetal substrate remains attached to the temporary carrier during thebonding of the first IMC stack to the second IMC stack, wherein thebonding includes metalbonding that is based at least in part on heat andwith a bonding temperature below the debonding temperature.
 18. Themethod of claim 17 wherein the first IMC stack comprises at least nickeland tin, and wherein the second IMC stack comprises at least nickel andtin.
 19. The method of claim 17, further comprising fabricating thepreformed metal substrate from a sheet of metal.
 20. The method of claim17 wherein the wafer is at least approximately six inches in diameter.21. The method of claim 17 wherein the first semiconductor materialcomprises an n-GaN material, the second semiconductor material comprisesa p-GaN material, and the active region comprises a multiple quantumwell region.
 22. The method of claim 17 wherein the preformed metalsubstrate has a thickness of about 50-300 μm.